Catalysis Frequently Asked Questions
- Comparison with homogeneous catalysts
- How do we measure the concentration of acid or basic groups?
- Should the catalyst be pretreated before use?
- How Amberlyst can be deactivated?
- How should the catalyst be loaded into the reactor ?
- Neutralization of active sites
- Organic fouling
- Loss of functional groups
- Loss of acidic group - desulfonation
- Loss of basic group by Hofmann's degradation
- Can spent Amberlyst be regenerated or reactivated for reuse?
- How should spent Amberlyst be unloaded?
- How should spent Amberlyst be disposed?
Comparison with homogeneous catalysts
Amberlyst™ are insoluble polymeric catalysts that can replace most of soluble strong acids and bases. The engineering advantages of using this class of heterogeneous catalysts increase manufacturing flexibility and reduce operating costs.
How do we measure the concentration of acid or basic groups?
Please consult our Master Test Methods to measure the density of acid groups [A4, USLetter] and of basic groups [A4, USLetter].
Should the catalyst be pretreated before use?
In general, no special pretreatment of the catalyst is required prior to loading into the reactor. Once the catalyst has been loaded, however, we usually recommend the catalyst be washed with deionized water to remove color bodies and organic leachables. See our "Startup procedure - loading and washing" page.
How should the catalyst be loaded into the reactor ?
See our "Startup procedure - loading and washing" page.
How Amberlyst can be deactivated?
The deactivation occurs in different ways, by
- Neutralization of active sites by contaminants
- Organic fouling
- Loss of functional groups
Neutralization of active sites
The hydrogen or hydroxyl ions can be replaced by other ions or can be neutralized respectively by basic or acidic compounds. In the case of strongly acidic resin catalysts, the poisons can be the cations from the groups I (ie. Na+) and II (ie. Ca2+) , metals such as iron or cupper and the amines or ammonia compounds. In the case of strongly basic resin catalysts, carbonates, chlorides or sulfates replace the hydroxyl groups.
This deactivation is reversible and the catalyst can be rejuvenated with appropriate regenerants to restore the hydrogen or hydroxyl ions.
When undesired by-products are formed and trapped in the polymeric matrix of the resin catalyst, they tend to mask the local active sites to the reactants. Consequently the catalyst drops its overall activity with an increase in volume and in dry mass and becomes more hydrophobic.
At elevated temperature, the desulfonation occurs for strongly acidic resin and the Hofman degradation for strongly basic resin catalysts. This deactivation is irreversible.
Loss of acidic group - desulfonation
Loss of basic group by Hofmann's degradation
The basic thermal degradation reaction is called Hofmann's reaction, shown here for a type 1 resin :
The basic thermal degradation reaction is called Hofmann's reaction, shown here for a type 1 resin :
Reaction (1) converts the SBA resin into a WBA, producing methanol as a by-product, and reaction (2) converts the ammonium group to an alcohol, which has no ion exchange capability, and produces trimethylamine as a by-product.
In reaction (1) the SBA resin loses strongly basic capacity, but the total capacity remains the same, whilst in reaction (2) all exchange capacity (for that particular functional group) is lost.
In practice, reaction (1) is approximately twice as frequent as reaction (2). Hofmann's reaction is catalysed by OH- ions. When the resin is constantly in salt form (e.g. in sugar decolourising applications) the degradation is much less severe. Type 2 SBA resins are much more sensitive than type 1, because the alcohol group weakens the bond to the nitrogen atom. The thermal stability of SBA resins declines as follows:
Cl > HCO3 > CO3 > OH.
Can spent Amberlyst be regenerated or reactivated for reuse?
Rejuvenation of catalyst is possible if the hydrogen or hydroxyl ions are replaced by other ionic constituents present in the reaction mixtures. Strongly acidic resins can be regenerated with sulfuric acid solution and strongly basic resins with caustic solution. When the catalyst is deactivated as a result of a "build up" of polymeric mass in the matrix, the recovery of the initial catalyst activity is extremely difficult. In the case of cation exchange resin catalysts that are fouled with high polymeric "crud", reactivation may require treatment with concentrated sulfuric acid at 90-100°C for a period of 4-8 hours. It also happens that some customers remove the polymeric catalyst and washed with an appropriate solvent to tentatively restore some activity of the catalyst. But generally, most customers do not regenerate the catalyst and some install sacrificial resin guard beds upfront to treat the reactant feeds.
How should spent Amberlyst be unloaded?
The unloading of the spent catalyst can be done by gravity or from the top
by vacuum. Before beginning any decommissioning operations, it is important
to confirm that there is adequate freeboard in the vessel to accommodate the
anticipated increase in catalyst bed volume. If the spent catalyst contains
hydrocarbons or volatile solvents, it should be purged first by hot nitrogen
purge or with steam prior to its unloading.
For more details click on the recommended procedure.
How should spent Amberlyst be disposed?
Disposal of the spent resin must be done in accordance with all applicable local, state, and federal regulations. Incineration and land filling are two options that have been used by customers.
